The process broadly consists of the following steps. Firstly the irradiated fuel is dissolved in nitric acid. Then solvent extraction using tributyl phosphate in odourless kerosene is employed with the liquid from dissolution, by which uranium and plutonium and some technetium are extracted but the bulk of the other fission products and higher actinides are retained in the aqueous raffinate. Then the solvent phase is backwashed and reductant to reduce the plutonium to the trivalent state is added so that, when a second solvent extraction using the same solvent is performed, uranium goes into the solvent phase whilst plutonium remains in the aqueous raffinate, primary separation thus having been performed. Where the nuclear fuel is oxide fuel, some pre-dissolution steps have to be performed, but otherwise the process is the same.
The present invention is concerned with the reducing step referred to in the previous paragraph and an object of the invention is to diminish the requirement for extraneous metal ions as reducing agents.